Water-cooled v-type engine, and motorcycle including same

ABSTRACT

A water-cooled V-type engine includes a first coolant passage for supplying a liquid coolant discharged from a water pump disposed proximate a first cylinder, to a water jacket of the first cylinder. The engine also includes a second coolant passage which is branched off from the first coolant passage, and which is provided for supplying coolant to a water jacket of a second cylinder. The engine design allows for a shortened coolant hose. The water pump may include an integral fluid conduit including a branching portion where said second coolant supply passage is branched from said first coolant supply passage, and a restricted portion proximate the branching portion. A motorcycle including a vehicle body frame is also described, where the water-cooled V-type engine is operatively attached to the vehicle body frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 USC 119 based on Japanesepatent application No. 2011-077676, filed on Mar. 31, 2011. The entiresubject matter of this priority document, including specification claimsand drawings thereof, is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cooling of the two cylinders of awater-cooled V-type engine, to a water-cooled V-type engine, and to amotorcycle including the V-type engine.

2. Background Art

In a conventionally known water-cooled V-type engine, a water pump isprovided on the lower rear side of the engine (see Patent Document 1,for example). Further, in another conventionally known water-cooledV-type engine, a water pump is provided at the upper portion of acrankcase (see Patent Document 2, for example).

[Patent Document 1] Japanese Patent Laid-Open No. 2003-90264

[Patent Document 2] Japanese Patent Laid-Open No. 2000-87758

However, in the water-cooled V-type engine described in Patent Document1 mentioned above, the water pump is located distantly from cylinderblocks and cylinder heads to be cooled, so that a coolant hose is verylong, causing a possibility of increase in manufacturing cost. Further,in the water-cooled V-type engine described in Patent Document 2mentioned above, a coolant hose can be made shorter than that of thewater-cooled V-type engine described in Patent Document 1, but it isdesired to further shorten the coolant hose.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstance,and it is accordingly an object of the present invention to provide awater-cooled V-type engine which can shorten a coolant hose.

Means for Solving the Problem

In accordance with a first aspect of the invention, there is provided awater-cooled V-type engine including first and second cylinders arrangedso as to form a V-shape; water jackets formed in cylinder blocks andcylinder heads of the first and second cylinders; and a water pump forfeeding a coolant from a radiator to the water jackets of the first andsecond cylinders, wherein the water pump is provided in the vicinity ofthe first cylinder; and the engine further includes a first coolantpassage for supplying the coolant discharged from the water pump to thewater jacket of the cylinder head of the first cylinder, and a secondcoolant passage which is branched from the first coolant passage, forsupplying the coolant to the water jacket of the cylinder head of thesecond cylinder.

In accordance with a second aspect of the invention, in addition to thefirst aspect, the water-cooled V-type engine further includes a firstdischarge opening for discharging the coolant that has first cooled thecylinder head of the first cylinder and has next cooled the cylinderblock of the first cylinder; a second discharge opening for dischargingthe coolant that has first cooled the cylinder head of the secondcylinder and has next cooled the cylinder block of the second cylinder;and a coolant return passage for supplying the coolant discharged fromthe first discharge opening and the second discharge opening to theradiator.

In accordance with a third aspect of the invention, in addition to thefirst aspect, the water pump is mounted on the cylinder head of thefirst cylinder and driven by a camshaft.

In accordance with a fourth aspect of the invention, in addition to thefirst aspect, a restricted portion is provided in the vicinity of abranching portion where the second coolant passage is branched from thefirst coolant passage.

In accordance with a fifth aspect of the invention in addition to thefourth aspect, the branching portion is formed integrally with a pumpbody of the water pump.

In accordance with a sixth aspect of the invention in addition to thefirst aspect, at least a part of a bolt hole for a bolt for mounting thewater pump is in communication with an inside space of the water pump,so that the bolt hole serves also as an air bleed hole.

In accordance with a seventh aspect of the invention in addition to thefirst aspect, an angle sensor for camshafts is mounted on the samesurface as the mounting surface of the first cylinder for mounting thewater pump.

In accordance with an eighth aspect of the invention in addition to thefirst aspect, the water-cooled V-type engine further includes a coolantrouting duct connected to the upper portion of the radiator forconnecting the water outlet of the radiator and the water pump; aconnection pipe communicating with the coolant routing duct; and apressure valve and an air bleeding mechanism both provided at the upperend of the connection pipe.

In accordance with a ninth aspect of the invention, in addition to theeighth aspect, the radiator includes a radiator core and right and lefttank portions respectively provided on the right and left sides of theradiator core; the coolant routing duct is connected to the upperportion of one of the right and left tank portions; and a coolantdischarge hose for supplying the coolant that has cooled the engine tothe radiator is connected to the lower portion of the one of the rightand left tank portions.

In accordance with a tenth aspect of the invention, in addition to theeighth aspect, the radiator is located on the front side of thewater-cooled V-type engine; the first cylinder is a forward-tiltedcylinder such that the cylinder head is located at a front upper portionof the water-cooled V-type engine; and the water outlet of the radiatorand the water pump are arranged in tandem as viewed in side elevation.

Effect of the Invention

According to the first aspect of the invention, the water pump isprovided in the vicinity of the first cylinder, and the engine includesthe first coolant passage for supplying the coolant discharged from thewater pump to the water jacket of the cylinder head of the firstcylinder and the second coolant passage which is branched from the firstcoolant passage, for supplying the coolant to the water jacket of thecylinder head of the second cylinder. Accordingly, a coolant hose forfeeding the coolant from the radiator to the cylinders can be shortened.Further, the coolant is first supplied to the cylinder heads, whichoperate at higher temperatures, so that the engine can be efficientlycooled.

According to the second aspect of the invention, the engine includes thefirst discharge opening for discharging the coolant that has firstcooled the cylinder head of the first cylinder and has next cooled thecylinder block of the first cylinder, the second discharge opening fordischarging the coolant that has first cooled the cylinder head of thesecond cylinder and has next cooled the cylinder block of the secondcylinder, and the third coolant passage for supplying the coolantdischarged from the first discharge opening and the second dischargeopening to the radiator. Accordingly, a coolant hose for feeding thecoolant from the cylinders to the radiator can be shortened.

According to the third aspect of the invention, the water pump ismounted on the cylinder head of the first cylinder and driven by thecamshaft. Accordingly, the water pump is located at substantially thesame level as that of the cylinder blocks and the cylinder heads.Accordingly, a vertical displacement of the coolant can be minimized, tofacilitate coolant flow.

According to the fourth aspect of the invention, the restricted portionis provided in the vicinity of the branching portion where the secondcoolant passage is branched from the first coolant passage. Accordingly,the flow rate of the coolant in the first coolant passage can becontrolled to be equal to the flow rate of the coolant in the secondcoolant passage.

According to the fifth aspect of the invention, the branching portion isformed integrally with the pump body of the water pump. Accordingly, thenumber of parts can be reduced and manufacturing cost can therefore bereduced.

According to the sixth aspect of the invention, at least a part of thebolt hole for the bolt for mounting the water pump is in communicationwith the inside space of the water pump, so that the bolt hole servesalso as an air bleed hole. Accordingly, a separate, dedicated air bleedis not required, and manufacturing cost can therefore be reduced.

According to the seventh aspect of the invention, the angle sensor forthe camshafts is mounted on the same surface as the mounting surface ofthe first cylinder for mounting the water pump. Accordingly, a deadspace formed by mounting the water pump can be effectively used.

According to the eighth aspect of the invention, the water-cooled V-typeengine includes the coolant routing duct connected to the upper portionof the radiator for connecting the water outlet of the radiator and thewater pump, the connection pipe communicating with the coolant routingduct, and the pressure valve and the air bleeding mechanism bothprovided at the upper end of the connection pipe. Accordingly, thepressure valve and the air bleeding mechanism can be located near theupper portion of the radiator and the water pump. As a result, apressure reduced by the water pump is applied to the pressure valve, sothat the pressure valve can be reduced in size and weight. Further,since the air bleeding mechanism can be located near the upper portionof the radiator, the connection pipe can be shortened to be reduced inweight.

According to the ninth aspect of the invention, the radiator includesthe radiator core and the right and left tank portions respectivelyprovided on the right and left sides of the radiator core, wherein thecoolant routing duct is connected to the upper portion of one of theright and left tank portions, and the coolant discharge hose forsupplying the coolant that has cooled the engine to the radiator isconnected to the lower portion of the one of the right and left tankportions. Accordingly, the coolant hoses are located on one side of thevehicle body, so that the workability in mounting the hoses to theradiator can be improved.

According to the tenth aspect of the invention, the radiator is locatedon the front side of the engine, and the first cylinder is aforward-tilted cylinder such that the cylinder head is located at afront upper portion of the water-cooled V-type engine. Further, thewater outlet of the radiator and the water pump are arranged in tandemas viewed in side elevation. Accordingly, the coolant routing duct canbe shortened.

For a more complete understanding of the present invention, the readeris referred to the following detailed description section, which shouldbe read in conjunction with the accompanying drawings. Throughout thefollowing detailed description and in the drawings, like numbers referto like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view of a motorcycle including a preferredembodiment of the water-cooled V-type engine according to the presentinvention.

FIG. 2 is a left side view of the engine shown in FIG. 1.

FIG. 3 is an enlarged vertical sectional view of the engine shown inFIG. 2.

FIG. 4 is an enlarged left side view of coolant passages and theirperiphery shown in FIG. 2.

FIG. 5 is a side view of a water pump shown in FIG. 4.

FIG. 6 is a cross section taken along the line A-A in FIG. 5.

FIG. 7 is a front view of a radiator shown in FIG. 2.

MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the water-cooled V-type engine according tothe present invention will now be described in detail with reference tothe drawings. The orientation of each drawing is the same as that of thereference symbols included therein. In the following description, theterms in relation to directions, such as front, rear, right, left,upper, and lower are the same as those viewed a from a vantage point ofan operator riding on the vehicle and facing forward. Further, in thedrawings, the arrow Fr denotes the front side of the vehicle, the arrowRr denotes the rear side of the vehicle, the arrow L denotes the leftside of the vehicle, the arrow R denotes the right side of the vehicle,the arrow U denotes the upper side of the vehicle, and the arrow Ddenotes the lower side of the vehicle.

In FIG. 1, reference numeral 10 generally denotes a motorcycle in thispreferred embodiment. The motorcycle 10 has a vehicle body frame 11. Thevehicle body frame 11 is composed of a head pipe 12 forming a front endmember, a pair of right and left main frames 13 extending rearward fromthe head pipe 12 so as to be inclined downward, a pair of right and leftengine hangers 14 extending downward from the lower surfaces of thefront portions of the right and left main frames 13, a pair of right andleft pivot plates 15 connected to the rear ends of the right and leftmain frames 13 and extending downward, and a pair of right and left seatframes 16 connected to the upper portions of the right and left pivotplates 15 and extending rearward so as to be inclined upward. An engine50 is mounted to the engine hangers 14 and the pivot plates 15.

The motorcycle 10 further includes a front fork 21 steerably supportedto the head pipe 12, a front wheel WF rotatably supported to the lowerends of the front fork 21, a steering handle 22 mounted to the upper endof the front fork 21, a swing arm 23 pivotably supported to the pivotplates 15, a rear wheel WR rotatably supported to the rear ends of theswing arm 23, a fuel tank 25 provided above the engine 50 so as to beinterposed between the right and left main frames 13, and an operatorseat 26 mounted on the right and left seat frames 16.

The motorcycle 10 further includes a front cowl 31, front side cowl 32,under cowl 33, rear cowl 34, headlight 35, rear-view mirror 36, frontfender 37, passenger seat 38, taillight 39, rear turn signal 40, rearfender 41, main step 42, pillion step 43, throttle body 44, air cleaner45, exhaust pipe 46, and muffler 47.

As shown in FIGS. 2 and 3, the engine 50 is a water-cooled V-typefour-cylinder engine, and it includes a crankcase 51, front and rearcylinders 52F and 52R provided at respective upper front and upper rearportions of the crankcase 51 so as to form a V-shape, a generator cover53 mounted on the left side surface of the crankcase 51, a clutch cover(not shown) mounted on the right side surface of the crankcase 51, andan oil pan 54 mounted on the lower surface of the crankcase 51. Further,a crankshaft 70 is rotatably supported in the crankcase 51, and orientedso as to extend in the lateral direction of the vehicle.

The front cylinder 52F includes a cylinder block 55F formed integrallywith the crankcase 51 at a front upper portion thereof, a cylinder head56F mounted on the upper end of the cylinder block 55F, and a cylinderhead cover 57F mounted on the upper end of the cylinder head 56F.Similarly, the rear cylinder 52R includes a cylinder block 55R formedintegrally with the crankcase 51 at a rear upper portion thereof, acylinder head 56R mounted on the upper end of the cylinder block 55R,and a cylinder head cover 57R mounted on the upper end of the cylinderhead 56R.

As shown in FIG. 3, the each of the cylinder blocks 55F and 55R has arespective cylinder bore 61 formed therein, and a piston 62 is slidablyfitted in each of the cylinder bores 61. The pistons 62 are connectedthrough connecting rods 63 to the crankshaft 70, respectively. Thecrankshaft 70 is rotationally driven by the reciprocating motion of thepistons 62.

Each of the cylinder heads 56F and 56R is formed with an intake port 64and an exhaust port 65, wherein an intake valve 64 a is provided in theintake port 64 and an exhaust valve 65 a is provided in the exhaust port65. Further, each of the cylinder heads 56F and 56R is provided with apair of camshafts 67 and 68 for respectively operating the intake valve64 a and the exhaust valve 65 a. The camshafts 67 and 68 are rotatablysupported on each of the cylinder heads 56F and 56R. Further, the lowersurface of each of the cylinder heads 56F and 56R is formed with acombustion chamber 66 therein, where a lower part of the combustionchamber is temporarily formed by an upper surface of the correspondingpiston 62, when it is at an upper range of travel.

As shown in FIG. 3, the cylinder blocks 55F and 55R are respectivelyformed with block water jackets 55 a and 55 b therein for conducting aflow of coolant therethrough. Similarly, the cylinder heads 56F and 56Rare respectively formed with cylinder head water jackets 56 a and 56 btherein for conducting a flow of coolant therethrough. Further, theblock water jacket 55 a (55 b) of the cylinder block 55F (55R) is incommunication with the corresponding cylinder head water jacket 56 a (56b) of the cylinder head 56F (56R).

As shown in FIGS. 2 and 4, a radiator 71 for cooling the coolant isprovided on the front side of the front cylinder 52F, and a water pump80 is mounted on the left side surface of the cylinder head 56F of thefront cylinder 52F. The water pump 80 is provided for feeding thecoolant from the radiator 71 to the water jackets 55 a, 55 b, 56 a, and56 b of the cylinders 52F and 52R.

The water pump 80 is connected to the left end of the lower camshaft 67of the front cylinder head 56 and is driven by this camshaft 67. A waterinlet of the water pump 80 and a water outlet of the radiator 71 areconnected by a coolant routing duct 72.

As shown in FIGS. 4 to 6, the water pump 80 includes a pump body 81 anda fluid conduit 82, which extends rearwardly from the pump body 81 so asto be inclined downwardly. The fluid conduit 82 has a first coolantsupply passage 83 formed therein for supplying the coolant dischargedfrom the water pump 80 to the water jacket 56 a of the front cylinderhead 56F.

The upper end portion of the pump body 81 is formed with a bolt hole 76for a bolt 75 for mounting the water pump 80. A part of the bolt hole 76is in communication with an inside space 77 (FIG. 6) of the water pump80. Accordingly, the bolt hole 76 serves also as an air bleed hole for acoolant passage 83.

The rear end portion of the fluid conduit 82 is formed with a branchingportion 84 for branching the coolant in the first coolant supply passage83. The branching portion 84 includes a first branch pipe 85 whichextends laterally inside of the engine, for supplying coolant to thewater jacket 56 a of the front cylinder head 56F. The branching portion84 also includes a second branch pipe 86 which extends toward the rearof the vehicle, for supplying coolant to the water jacket 56 b of therear cylinder head 56R. The branching portion 84 and the fluid conduit82 are both formed integrally with the pump body 81 of the water pump80.

A coolant-receiving pipe 88 is mounted on the left side surface of therear cylinder head 56R so as to extend frontward of the vehicle. Thecoolant-receiving pipe 88 is connected through a coolant supply hose 87to the second branch pipe 86. The coolant-receiving pipe 88 functions tosupply the coolant fed from the second branch pipe 86 to the waterjacket 56 b of the rear cylinder head 56R. In this preferred embodiment,the second branch pipe 86, the coolant supply hose 87, and the innersurface of the coolant-receiving pipe 88 form a second coolant supplypassage 89.

The second branch pipe 86 is formed with a restricted portion 86 a overthe entire circumference thereof so that the cross section of therestricted portion 86 a is substantially trapezoidal. The restrictedportion 86 a functions to reduce the inner diameter of the secondcoolant supply passage 89 at a portion in the vicinity of the firstbranch pipe 85.

Referring again to FIG. 4, it will be seen that the left side surface ofthe front cylinder block 55F is formed with a first discharge opening 91for discharging the coolant that has first cooled the water jacket 56 aof the front cylinder head 56F and has next cooled the water jacket 55 aof the front cylinder block 55F. Similarly, the left side surface of therear cylinder block 55R is formed with a second discharge opening 92 fordischarging the coolant that has first cooled the water jacket 56 b ofthe rear cylinder head 56R and has next cooled the water jacket 55 b ofthe rear cylinder block 55R.

A coolant discharge pipe 93 is mounted on the left side surfaces of thecylinder blocks 55F and 55R so as to extend in the longitudinaldirection of the vehicle. The coolant discharge pipe 93 has a thirdcoolant passage 94 for receiving the coolant discharged from the firstand second discharge openings 91, 92 and for supplying them to theradiator 71. The front end portion of the coolant discharge pipe 93 isconnected through a coolant discharge hose 73 to a water inlet of theradiator 71. Accordingly, the coolant that has cooled the engine 50 isintroduced through the coolant discharge pipe 93 and the coolantdischarge hose 73 to the radiator 71.

In the engine 50 mentioned above, the coolant discharged from the waterpump 80 flows in the following order: the first coolant supply passage83 of the fluid conduit 82; the first branch pipe 85; the water jacket56 a of the front cylinder head 56F; the water jacket 55 a of the frontcylinder block 55F; the first discharge opening 91; and the thirdcoolant passage 94 of the coolant discharge pipe 93.

The coolant discharged from the water pump 80 also flows in thefollowing order: the first coolant supply passage 83 of the fluidconduit 82; the second coolant supply passage 89 of the second branchpipe 86, the coolant supply hose 87, and the coolant-receiving pipe 88;the water jacket 56 b of the rear cylinder head 56R; the water jacket 55b of the rear cylinder block 55R; the second discharge opening 92; andthe third coolant passage 94 of the coolant discharge pipe 93.

The coolant from the coolant discharge pipe 93 flows in the followingorder: the coolant discharge hose 73; the radiator 71; and the coolantrouting duct 72. The coolant is finally returned to the water pump 80.

As shown in FIG. 4, in the preferred embodiment, an angle sensor 69 forthe camshafts 67 and 68 is mounted on the left side surface of thecylinder head cover 57F of the front cylinder 52F at a position on theupper rear side of the water pump 80.

In this preferred embodiment, as shown in FIGS. 2 and 7, the radiator 71includes a radiator core 71 a and right and left tank portions 71R and71L respectively provided on the right and left sides of the radiatorcore 71 a. The coolant routing duct 72 is connected to the upper portionof the left tank portion 71L, and the coolant discharge hose 73 isconnected to the lower portion of the left tank portion 71L. The arrowshown by reference symbol B in FIG. 7 represents the flow of the coolantin the radiator 71.

The coolant routing duct 72 is provided with a connection pipe 95communicating therewith, a filler neck 96 provided at the upper end ofthe connection pipe 95, a pressure valve 97 provided in the filler neck96, and a filler cap (air bleeding mechanism) 98 for closing the upperend opening of the filler neck 96. In FIG. 2, reference numeral 99denotes a pipe connected to a reservoir tank.

As shown in FIG. 2, the radiator 71 is located on the front side of theengine 50, and the front cylinder 52F is a forward-tilted cylinder suchthat the cylinder head 56F is located at a front upper portion of theengine 50. Further, the water outlet of the radiator 71 and the waterpump 80 are arranged in tandem as viewed in side elevation.

According to the water-cooled V-type engine 50 of this preferredembodiment mentioned above, the water pump 80 is provided on the frontcylinder 52F, and the engine 50 includes the first coolant supplypassage 83 for supplying the coolant discharged from the water pump 80to the water jacket 56 a of the cylinder head 56F of the front cylinder52F and the second coolant supply passage 89 which is branched from thefirst coolant supply passage 83, for supplying the coolant to the waterjacket 56 b of the cylinder head 56R of the rear cylinder 52R.Accordingly, the coolant hoses 72 and 87 for feeding the coolant fromthe radiator 71 to the cylinders 52F and 52R can be shortened. Further,the coolant is first supplied to the cylinder heads 56F and 56R whichbecome higher temperatures, so that the engine 50 can be efficientlycooled.

According to the water-cooled V-type engine 50 of this preferredembodiment, the engine 50 includes the first discharge opening 91 fordischarging the coolant that has first cooled the cylinder head 56F ofthe front cylinder 52F and has next cooled the cylinder block 55F of thefront cylinder 52F, the second discharge opening 92 for discharging thecoolant that has first cooled the cylinder head 56R of the rear cylinder52R and has next cooled the cylinder block 55R of the rear cylinder 52R,and the third coolant passage 94 for supplying the coolant dischargedfrom the first discharge opening 91 and the second discharge opening 92to the radiator 71. Accordingly, the coolant hose 73 for feeding thecoolant from the cylinders 52F and 52R to the radiator 71 can beshortened.

According to the water-cooled V-type engine 50 of this preferredembodiment, the water pump 80 is mounted on the cylinder head 56F of thefront cylinder 52F and driven by the camshaft 67. Accordingly, the waterpump 80 is located at substantially the same level as that of thecylinder blocks 55F and 55R and the cylinder heads 56F and 56R.Consequently, a vertical displacement of the coolant can be reduced tothereby facilitate the flow of the coolant.

According to the water-cooled V-type engine 50 of this preferredembodiment, the second branch pipe 86 is formed with the restrictedportion 86 a in the vicinity of the branching portion 84 where thesecond coolant supply passage 89 is branched from the first coolantsupply passage 83. Accordingly, the flow rate of the coolant in thefirst coolant supply passage 83 can be controlled to be equal to theflow rate of the coolant in the second coolant supply passage 89.

According to the water-cooled V-type engine 50 of this preferredembodiment, the branching portion 84 is formed integrally with the pumpbody 81 of the water pump 80. Accordingly, the number of parts can bereduced and a manufacturing cost can therefore be reduced.

According to the water-cooled V-type engine 50 of this preferredembodiment, a part of the bolt hole 76 for the bolt 75 for mounting thewater pump 80 is in communication with the inside space 77 of the waterpump 80, so that the bolt hole 76 serves also as an air bleed hole.Accordingly, any dedicated hole as an air bleed hole is not required anda manufacturing cost can therefore be reduced.

According to the water-cooled V-type engine 50 of this preferredembodiment, the angle sensor 69 for the camshafts 67 and 68 is mountedon the left side surface of the cylinder head cover 57F of the frontcylinder 52F which surface is the same surface as the mounting surfacefor the water pump 80. Accordingly, a dead space formed by mounting thewater pump 80 can be effectively used.

According to the water-cooled V-type engine 50 of this preferredembodiment, the engine 50 includes the coolant routing duct 72 connectedto the upper portion of the left tank portion 71L of the radiator 71 forconnecting the water outlet of the radiator 71 and the water pump 80,the connection pipe 95 communicating with the coolant routing duct 72,and the pressure valve 97 and the filler cap 98 both provided at theupper end of the connection pipe 95. Accordingly, the pressure valve 97and the filler cap 98 can be located near the upper portion of theradiator 71 and the water pump 80. As a result, a pressure reduced bythe water pump 80 is applied to the pressure valve 97, so that thepressure valve 97 can be reduced in size and weight. Further, since thefiller cap 98 can be located near the upper portion of the radiator 71,the connection pipe 95 can be shortened to be reduced in weight.

According to the water-cooled V-type engine 50 of this preferredembodiment, the radiator 71 includes the radiator core 71 a and theright and left tank portions 71R and 71L respectively provided on theright and left sides of the radiator core 71 a, wherein the coolantrouting duct 72 is connected to the upper portion of the left tankportion 71L, and the coolant discharge hose 73 is connected to the lowerportion of the left tank portion 71L. Accordingly, the coolant hoses 72and 73 are located on one side of the vehicle body, so that theworkability in mounting the hoses to the radiator 71 can be improved.

According to the water-cooled V-type engine 50 of this preferredembodiment, the radiator 71 is located on the front side of the engine50, and the front cylinder 52F is a forward-tilted cylinder such thatthe cylinder head 56F is located at a front upper portion of the engine50. Further, the water outlet of the radiator 71 and the water pump 80are arranged in tandem as viewed in side elevation. Accordingly, thecoolant routing duct 72 can be shortened.

The present invention is not limited to the above preferred embodiment,but various modifications may be made without departing from the scopeof the present invention.

1. A water-cooled V-type engine, comprising: first and second cylindersarranged so as to form a V-shape, said first cylinder comprising a firstcylinder block having a first block water jacket formed therein and afirst cylinder head attached to said first cylinder block and having afirst cylinder head water jacket formed therein in fluid communicationwith the first block water jacket; said second cylinder comprising asecond cylinder block having a second block water jacket formed thereinand a second cylinder head attached to said second cylinder block andhaving a second cylinder head water jacket formed therein in fluidcommunication with the second block water jacket; and a water pump fortransferring coolant from a radiator to the water jackets of said firstand second cylinders, said water pump situated proximate said firstcylinder; wherein said engine further includes a first coolant supplypassage for supplying coolant from said water pump to the first cylinderhead water jacket, and a second coolant supply passage which is branchedfrom said first coolant supply passage for supplying coolant to saidsecond cylinder head water jacket.
 2. The water-cooled V-type engineaccording to claim 1, further comprising: a first discharge openingformed in the first cylinder block for discharging coolant that hasfirst cooled said first cylinder head and has then cooled said firstcylinder block; a second discharge opening formed in the second cylinderblock for discharging coolant that has first cooled said second cylinderhead and has then cooled said second cylinder block; and a dischargepipe extending between the first and second cylinder blocks, saiddischarge pipe having a coolant return passage formed therein forrouting coolant from said first and second discharge openings towardsaid radiator.
 3. The water-cooled V-type engine according to claim 1,wherein said water pump is mounted on said first cylinder head anddriven by a camshaft.
 4. The water-cooled V-type engine according to ofclaim 1, further comprising a fluid conduit comprising a branchingportion where said second coolant supply passage is branched from saidfirst coolant supply passage, and a restricted portion proximate saidbranching portion.
 5. The water-cooled V-type engine according to claim4, wherein said fluid conduit is formed integrally with a pump body ofsaid water pump.
 6. The water-cooled V-type engine according to claim 1,wherein said water pump has a plurality of bolt holes formed therein forreceiving mounting bolts, and wherein one of said bolt holes is in fluidcommunication with an inside space of said water pump, so that said bolthole also serves as an air bleed hole.
 7. The water-cooled V-type engineaccording to claim 1, wherein said water pump is mounted on a mountingsurface of said first cylinder, and wherein a cam angle sensor forsensing a rotary position of a camshaft is also mounted on the mountingsurface of said first cylinder.
 8. The water-cooled V-type engineaccording to claim 1, further comprising: a coolant routing ductconnected to an upper portion of said radiator for conveying coolantfrom said radiator toward said water pump; a connection pipecommunicating with said coolant routing duct; and a pressure valve andan air bleeding mechanism both provided at an upper end of saidconnection pipe.
 9. The water-cooled V-type engine according to claim 8,wherein: the radiator includes a radiator core and right and left tankportions respectively provided on right and left sides of said radiatorcore; said coolant routing duct is connected to an upper portion of oneof said right and left tank portions; and a coolant discharge hose forsupplying coolant from said engine to said radiator is operativelyconnected to a lower portion of the same tank portion to which saidcoolant routing duct is connected.
 10. The water-cooled V-type engineaccording to claim 8, wherein: the radiator is located on the front sideof said water-cooled V-type engine; said first cylinder is aforward-tilted cylinder such that said cylinder head is located at afront upper portion of said water-cooled V-type engine; and wateroutlets of said radiator and said water pump are arranged in tandem asviewed in side elevation.
 11. A motorcycle comprising a vehicle bodyframe and a V-type engine operatively attached to said vehicle bodyframe, said engine comprising: first and second cylinders arranged so asto form a V-shape, said first cylinder comprising a first cylinder blockhaving a first block water jacket formed therein and a first cylinderhead attached to said first cylinder block and having a first cylinderhead water jacket formed therein in fluid communication with the firstblock water jacket; said second cylinder comprising a second cylinderblock having a second block water jacket formed therein and a secondcylinder head attached to said second cylinder block and having a secondcylinder head water jacket formed therein in fluid communication withthe second block water jacket; and a water pump for transferring coolantfrom a radiator to the water jackets of said first and second cylinders,said water pump situated proximate said first cylinder; wherein saidengine further includes a first coolant supply passage for supplyingcoolant from said water pump to the first cylinder head water jacket,and a second coolant supply passage which is branched from said firstcoolant supply passage for supplying coolant to said second cylinderhead water jacket.
 12. The motorcycle according to claim 11, furthercomprising: a first discharge opening formed in the first cylinder blockfor discharging coolant that has first cooled said first cylinder headand has then cooled said first cylinder block; a second dischargeopening formed in the second cylinder block for discharging coolant thathas first cooled said second cylinder head and has then cooled saidsecond cylinder block; and a discharge pipe extending between the firstand second cylinder blocks, said discharge pipe having a coolant returnpassage formed therein for routing coolant from said first and seconddischarge openings toward said radiator.
 13. The motorcycle according toclaim 11, wherein said water pump is mounted on said first cylinder headand driven by a camshaft.
 14. The motorcycle according to claim 11,further comprising a fluid conduit comprising a branching portion wheresaid second coolant supply passage is branched from said first coolantsupply passage, and a restricted portion proximate said branchingportion.
 15. The motorcycle according to claim 14, wherein said fluidconduit is formed integrally with a pump body of said water pump. 16.The motorcycle according to claim 11, wherein said water pump has aplurality of bolt holes formed therein for receiving mounting bolts, andwherein one of said bolt holes is in fluid communication with an insidespace of said water pump, so that said bolt hole also serves as an airbleed hole.
 17. The motorcycle according to claim 11, wherein said waterpump is mounted on a mounting surface of said first cylinder, andwherein a cam angle sensor for sensing a rotary position of a camshaftis also mounted on the mounting surface of said first cylinder.
 18. Themotorcycle according to claim 11, further comprising: a coolant routingduct connected to an upper portion of said radiator for conveyingcoolant from said radiator toward said water pump; a connection pipecommunicating with said coolant routing duct; and a pressure valve andan air bleeding mechanism both provided at an upper end of saidconnection pipe.
 19. The motorcycle according to claim 18, wherein: theradiator includes a radiator core and right and left tank portionsrespectively provided on right and left sides of said radiator core;said coolant routing duct is connected to an upper portion of one ofsaid right and left tank portions; and a coolant discharge hose forsupplying coolant from said engine to said radiator is operativelyconnected to a lower portion of the same tank portion to which saidcoolant routing duct is connected.
 20. The motorcycle according to claim18, wherein: the radiator is located on the front side of saidwater-cooled V-type engine; said first cylinder is a forward-tiltedcylinder such that said cylinder head is located at a front upperportion of said water-cooled V-type engine; and water outlets of saidradiator and said water pump are arranged in tandem as viewed in sideelevation.